Crop farming typically involves the sowing, fertilisation and harvesting of crop plants in a paddock. Modern day crop farming makes extensive use of automotive farm machinery, such as tractors, which are used to pull field-working implements, such as ploughs or fertilising rigs etc. The width of the field-working implement is generally greater than the width of the tractor. In operation the tractor is driven up and down the paddock in passes which follow parallel lines. However if the passes are too close together, that is closer than the working width of the implement, then a problem arises in that over consecutive passes the implement is partially back over a strip of paddock processed during the last pass. Hence an undesirable overlap occurs. Alternatively, if the passes are too far apart then another problem arises in that a strip of unprocessed paddock is left between consecutive passes of the implement.
Consequently it is desirable that the tractor passes up and down the field along lines which are parallel and offset from each other by approximately the working width of the implement being towed. Adhering to such a strategy results in savings in the amount of fuel used to power the vehicle as the number of passes required to process a given area is reduced. Savings are also made in the amount of pesticides, machinery wear and tear and labour expended in processing a given area.
However, ensuring that the offset between consecutive passes of the tractor is continuously maintained equal to the working width of the implement requires the exercise of skill and endurance by the driver of the tractor. Factors such as varying seasonal conditions, undulating terrain, driver fatigue and such like may result in the driver inaccurately estimating the correct starting point of a pass, so that the offset from an adjacent pass is incorrect, or may result in the vehicle being driven non-parallel to the first pass. As a result overlap or separation between the areas processed during consecutive passes of the vehicle up and down the paddock may occur.
In U.S. Pat. No. 4,515,221 there is described a guidance system for a tractor which makes use of a gyroscopic system to monitor the direction of motion of an agricultural vehicle. However the invention requires that the gyroscopic system maintains a platform, on which two accelerometers are mounted, in perfectly horizontal disposition and so is technically difficult to implement and lacking in ruggedness and accuracy.
In U.S. Pat. No. 5,938,709 there is described a field mapping system for an agricultural vehicle, however the system does not directly aid in addressing the problem of maintaining a correct offset between consecutive passes of an agricultural vehicle as described above.
It is an object of the present invention to provide a system for aiding in the navigation of an agricultural vehicle so that consecutive passes of the vehicle are optimally offset.